Current legislation requires the use of contained piping systems when transporting contaminants underground. This legislation is particularly applicable to the fuel-handling market. Fuel, e.g., gasoline, is stored underground in tanks and is then piped to overground fuel pumps. To prevent contamination of the surrounding ground, the legislation requires that a secondary pipe, also referred to as merely a xe2x80x9csecondary,xe2x80x9d is used to encase the main pipe and contain any leakage from the main pipe, also referred to as the xe2x80x9cprimary.xe2x80x9d As a result, since the tank is a low point in the system, any leakage contained in the second pipe flows, due to gravity, back to the tank. Such systems are sometimes referred to as dual containment systems.
This legislation has given rise to the need for a secondary piping system which is easy to install and economical. A substantial portion of the cost of these systems is driven by the technique used to join the secondary pipes forming the containment system.
In an assembly of contained piping, it is desired, and often required, that the primary connection be visible during an initial pressure test of the system to insure integrity at test pressures. Typically, the secondary is designed with a gap over the points where the primary is joined to allow inspection of the joint under test pressures. Closure of this gap can become difficult depending on the intended service and system design. Usually this gap is closed with a two-piece fitting (xe2x80x9cclam-shellxe2x80x9d design) such as by manufacturing the secondary fitting element in two length-wise elements, i.e., split longitudinally into equal halves. However, the junction between the two halves create a low strength point which usually will not perform to the level of the rest of the system. Even though the secondaries are usually rated for low pressures, there are occasions in which the secondary is required to be rated at the same pressure as the primary. The joining methods to resist pressures at primary ratings are costly.
It is therefore desirable to provide a cost effective and high strength technique for closing the secondary at the joints which is capable of operating under the same pressures as the primary.
According to one embodiment of the invention, a double containment pipe connection is provided which includes an inner primary pipe and an outer secondary pipe with a fluid passage between the pipes, a fitting including an inner tube and an outer tube with a fluid passage between the tubes, an intermediate diameter portion adjacent to the end of the outer tube of the fitting having a diameter intermediate between the inside diameter and the outside diameter of the outer tube, and a sealing reducer. The sealing reducer includes a smaller diameter end having an inside diameter sufficiently larger than the outside diameter of the outer secondary pipe to slide over the outside of the outer secondary pipe, and a larger diameter end having an inside diameter sufficiently larger than the outside diameter of the inner tube to permit fluid flow therebetween. A first seal is provided between the smaller diameter end of the reducer and the outside of the outer secondary pipe, and a second seal is provided between the larger diameter end of the reducer and the intermediate diameter portion of outer tube of the fitting.
According another embodiment, the intermediate diameter portion includes a thread on an inside surface of outer tube, and the second seal includes an elastomeric ring having an inside diameter sufficiently larger than the outside diameter of the inner tube to permit fluid flow therebetween, and a thread is provided on the reducer for compressing the second seal between the reducer and the second tube.
According to another embodiment, the intermediate diameter portion is a cylindrical surface on the outer tube, and the second seal is provided by an adhesive cement between the intermediate diameter portion and the larger diameter end of the reducer. Preferably, a split ring or a pair of 180xc2x0 wedges are positioned around the annular lip of the secondary pipe and adhered to the secondary pipe with an adhesive cement.
According to another embodiment, a sealing fitting for use in a double containment connection is provided which includes two complementary semi-annular portions which fit together to form an annular fitting having a smaller diameter end and a larger diameter end, each semi-annular portion having at each end a substantially flat mating surface extending from an inner to an outer surface of the semi-annular portion at an acute angle to tangent to the inside diameter of the semi-annular portion.
According to another embodiment, a sealing fitting for use in a double containment connection is provided which includes first and second complementary semi-annular portions which fit together to form an annular fitting having a smaller diameter end and a larger diameter end, each semi-annular portion having at each end a mating surface including a tongue and a groove, wherein each tongue on the first semi-annular portion is adapted to fit closely in a corresponding groove on the second semi-annular portion, and wherein each tongue on the second semi-annular portion is adapted to fit closely in a corresponding groove on the first semi-annular portion.